Process for metallizing substrates

ABSTRACT

SUBSTRATE ARE PLATED WITH METALS BY SUBJECTING THE SUBSTRATES TO ELEMENTAL PHOSPHORUS AND SUBJECTING THE THUS TREATED SUBSTRATE TO A METAL SALT BATH COMPRISING A METAL SALT, AN AMINE, AN ALKALI METAL HYDROXIDE AND AMMONIUM HYDROXIDE. THE RESULTING TREATED SUBSTRATES CAN BE ELECTROLESS PLATED AND/OR ELECTROPLATED BY CONVENTIONAL TECHNIQUES.

3 666 637 PROCESS FOR METALlJZlNG SUBSTRATES John K. MacKay, Niagara Falls, Ontario, Canada, as-

signor to Hooker Chemical Corporation, Niagara Falls,

X. No Drawing. Filed Jan. 30, 1970, Ser. No. 7,257 Int. Cl. C23b 5/60 US. Cl. 20430 9 Claims ABSTRACT OF THE DISCLOSURE Substrates are plated with metals by subjecting the substrates to elemental phosphorus and subjecting the thus treated substrate to a metal salt bath comprising a metal salt, an amine, an alkali metal hydroxide and ammonium hydroxide. The resulting treated substrates can be electroless plated and/or electroplated by conventional techniques.

BACKGROUND OF THE INVENTION There is a rapidly increasing demand for metal plated articles, for example, in the production of low cost plastic articles that have a simulated metal appearance. Such articles are in demand in such industries as automotive, home appliance, radio and television and for use in decorative containers and the like. A new process for the metallizing of plastics has been developed which briefly comprises subjecting a substrate to elemental white phosphorus, subjecting the thus treated substrate to a metal salt or complex thereof, and thereafter electroless plating and/or electroplating the resulting treated substrate. In copending application Ser. No. 694,122, filed Dec. 28, 1967, now Pat. No. 3,616,295, an improved metal salt bath is provided in which a small amount of sodium hydroxide is added to the bath. This allows the bath to be operated at room temperature. It has been observed that when an amine is employed as the 'complexing agent in this improved metal salt bath of the copending application, the electroplated sample has a tendency to develop on standing, even at room temperature, liquid filled blisters at the interface of the electroplate. Since it is known that, for example, an aqueous solution of an amine such as ethylene diamine will dissolve metallic nickel even in the absence of air, it is theorized that the development of the liquid filled blisters can be attributed to the slow attack of the amine on the electroplated metal. It has now been found that these liquid filled blisters can be substantially avoided by further modifying the improved bath of the copending application by the addition of ammonium hydroxide. The metal salt bath of this invention also has the additional advantage that it may be stirred vigorously without effecting the adhesion of the plated metal to the substrate.

It is the object of this invention to provide an improved process for the metal plating of substrates. It is also the object of this invention to provide an improved metal salt bath which can be employed in metallizing substrates. A further object of the invention is to provide an improved process whereby the liquid filled blisters of the previous process can be substantially avoided. A still further object of the invention is to provide an improved metal salt bath which can be vigorously stirred without efiecting the adhesion of the plated metal to the substrate. Other objects will become apparent to those skilled in the art from the following detailed description.

SUMMARY OF THE INVENTION This invention relates to an improved process for the metal plating of substrates. More particularly, the invention relates to an improved process comprising subjecting 3,666,637. Patented May 30, 1972 a substrate to elemental phosphorus and thereafter subjecting the thus treated substrate to a metal salt solution comprising a metal salt, an amine, an alkali metal hydroxide and ammonium hydroxide. The resulting treated substrate can be electroless plated and/or electroplated by conventional techniques.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of this invention is applicable to substrates, such as plastics and to other substantially non-metallic substrates. Suitable substrates include, but are not limited to, cellulosic and ceramic materials such as cloth, paper, wood, cork, cardboard, clay, procelain, leather, porous glass, asbestos, cement, and the like.

Typical plastics to which the process of this invention is applicable include the homopolymers and copolymers of ethylenically unsaturated aliphatic, alicyclic and aromatic hydrocarbons such as polyethylene, polypropylene, polybutene, ethylenepropylene copolymers; copolymers of ethylene or propylene with other olefins, polybutadiene; polymers of butadiene, polyisoprene, polystyrene and polymers of pentene, hexene, cyclopentadiene, methylstyrene, andthe like. Other polymers useful in the invention include chlorinated polypropylene and methylene; polyindene, indenecoumarone resins; polymers of acrylate esters and polymers of methacrylate 'esters, acrylate and methacrylate resins such as ethyl acrylate; alkyd resins; cellulose derivatives such as cellulose acetate; cellulose acetate butyrate, cellulose nitrate, ethyl cellulose; epoxy resins; furan resins (furfuryl alcohol or furfural ketone): hydrocarbon resins from petroleum, isobutylene resins (polyisobutylene); isocyanate resins (polyurethanes); polyurea resins; melamine resins such as melamine-formaldehyde; oleoresins, phenolic resins such as phenol-formaldehyde; polyamide polymers, such as polyamides, poly-amideepoxy and particularly long chain synthetic polymeric amides containing recurring carbonamide groups as an integral part of the main polymer chain; polyester resins such as unsaturated polyesters of dibasic acids and dihydroxy compounds, and polyester elastomer and resorcinol resins such as resorcinol-formaldehyde; rubbers such as natural rubber, synthetic polyisoprene reclaimed rubber, chlorinated rubber, polybutadiene; polysulfides (Thiokol); terpene resins; urea resins; vinyl resins such as polymers of vinyl acetal; polyvinylchloride; polyformaldehyde; polyphenylene oxide; polymers of diallylphthalates and phthalates; polycarbonates of phosgene or thiophosgene and dihydroxy compounds such as bisphenols, thermoplastic polymers of bisphenols and epichlorohydrin (tradename Phenoxy polymers); graft copolymers of polymers of unsaturated hydrocarbons and an unsaturated monomer, such as graft copolymers of polybutadiene, styrene and acrylonitrile, commonly called ABS resin; ABS-polyvinylchloride polymers, recently introduced under the trade name of Cycovin; and acrylic polyvinyl chloride polymers, known by the trade name of Kydex 100.

The polymers can be used in the unfilled condition, or with fillers such as glass fiber, glass powder, glass beads, asbestos, talc and other mineral fillers,"wood flour and other vegetable fillers, carbon in its various forms, dyes, pigments, waxes and the like.

The substrates can be in various physical forms, such as shaped articles, for example, moldings, sheets, rods, and the like; fibers, films, and fabrics, and the like and of various thickness.

In the first step of the preferred process, the substrate is subjected to elemental white phosphorus, which includes the various impure or commercial grades sometimes referred to as yellow phosphorus. The phosphorus can be utilized'in the vapor phase, as a liquid or dissolved in a solvent. Suitable solvents or diluents for the elemental phosphorus are solvents that dissolve elemental phosphorus and which preferably swell the surface of a plastic without detrimentally affecting the surface of the plastic.

When a solution of phosphorus is employed in the process, the solution concentration is generally in the range from about 0.0001 weight percent of phosphorus based on the weight of the solution up to a saturated solution and preferably from about 0.5 to about 2.5 percent. Prior to subjecting the substrate to the elemental phosphorus, in gaseous, liquid or solution, the surface of the article should be clean. When a solution is used; the solvent generally serves to clean the surface. A solvent wash may be desirable when gaseous or liquid phosphorus is employed. However, it is not necessary to sub.- ject the substrate to special treatment such as etching, polishing and the like. The phosphorus treatment is generally conducted at a temperature below the softening point of the substrate, and below the boiling point of the solvent, if a solvent is used. Generally, the temperature is in the range of about 10 to about 135 degrees centigrade, but preferably in the range of about 10 to about 100 degrees centigrade. The contact time varies depending on the nature of the substrate, the solvent and temperature, but is generally in the range of about one second to one hour or more, preferably in the range of about one to ten minutes.

As a result of the first treatment step, the phosphorus is deposited or nucleated at the surface of the substrate. By this is meant that the phosphorus can be located on the surface, embedded in the surface and embedded beneath the surface of the substrate. The location of the phosphorus is somewhat dependent on the action of the solvent and reaction conditions on the surface.

Following the first treatment step, the substrate can be subjected to water and/or aqueous solution of a surfactant, as disclosed in copending application S.N. 67l,- 337, filed Sept. 28, 1967, and then can be dried by merely exposing the substrate to the atmosphere or to inert atmospheres such as nitrogen, carbon dioxide, and the like, or by drying the surface with radiant heaters or in a conventional oven. Drying times can vary considerably, for example, from one second to 30 minutes or more, preferably seconds to minutes, more preferably 5 seconds to 20 seconds. The rinsing and drying steps are optional.

In the second treatment of the process, the phosphorustreated substrate is subjected to a bath containing a solution of an amine complex of a metal salt containing an 4 metal salts include copper sulfate, copper chloride, silver nitrite, nickel sulfate and nickel chloride.

The metal salts are complexed with an amine that produces a solution having a basic pH 7). Useful amine complexes include the mono-(ethylene diamine), bis (ethylene diamine), tris-(ethylene diamine), bis-(1,2- propane diamine), bis-(1,3-propane diamine), triethylene tetraamine, and the like amines.

The foregoing metal salt complexes are used in ionic media, preferably in aqueous solutions. However, nonaqueous media can be employed such as alcohols, for example, methyl alcohol, ethyl alcohol, and the like; cyclic ethers, for example, tetrahydrofuran, dioxane and the like. Mixtures of alcohol and water can be used. Also useful are ionic mixtures of alcohol with other miscible solvents. The solution concentration is generally in the range from about 0.1 weight percent metal salt complex based on the total Weight of the solution up to a saturated solution, preferably from about 1 to about 10 alkali metal hydroxide and NH OH which is capable of reacting with the phosphorus to form a metal p-hospbide. The term metal phosphide, as used herein, means the metal-phosphorus coating which is formed at the surface of the substrate. Without being limited to theory, the metal phosphide may be an ionic compound or a solution (alloy). The metals generally employed are those of Groups -IB, II-B, IV-B, V-B, VI-B, VII-B and VIII of the Periodic Table appearing on pages 60-6 1 of Ianges Handbook of Chemistry (Revised Tenth Edition). The preferred metals are copper, silver, gold, chromium, manganese, cobalt, nickel, palladium, titanium, zirconium, vanadium, tantalum, cadmium, tungsten, molybdenum, and the like.

The metal salts that are used in the invention can contain a wide variety of anions. Suitable anions include the anions of mineral acids such as sulfate, chloride, bromide, iodide, fluoride, nitrate, phosphate, chlorate, perchlorate, borate, carbonate, cyanide, and the like. Also useful are the anions of organic acids such as formate, acetate, citrate, butyrate, valorate, caproate, heptylate, palmitate, dimethylglyoxime, and the like. Generally the anions of organic acids contain 1 to 18 carbon atoms. Some useful weight percent salt complex. The pH of the metal salt complex solution can range from about 4 to 14 but is generally maintained in the basic range i.e., greater than 7.0 and preferably from about 10 to about 13.

The metal salt complex solution also contains an alkali metal (Group I-A) hydroxide. Thus, the solution can contain lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide and mixtures thereof. The concentrations of the amine, alkali metal hydroxide and ammonium hydroxide can be varied within wide limits as long as the metal remains in solution. Usable concentrations can readily be calculated from the known formation constants and known solubilities of the various metal complexes present in the solution. In general, the amine, alkali metal hydroxide and ammonium hydroxide are employed such that the concentration of each is at least 0.01 molar.

The step of subjecting the phosphorus treated substrate to the solution of metal salt is generally conducted at a temperature below the softening point of the substrate and below the boiling point of the solvent, if one is used. Generally the temperature is in the range of about 10 to 110 C. preferably from about 20 to C. The time of contact can vary considerably depending on the nature of the substrate, the characteristics of the metal salt solution employed and the contact temperature. However, the time of contact is generally in the range of about 0.1 to 3 0 minutes preferably about 5 to 10 minutes.

The surfaces that result from contacting the phosphorus treated substrate with the metal salt solution can be subjected to a process that has become known in the art as electroless plating or chemical plating. In a typical electroless plating process, a catalytic surface is contacted with a solution of metal salt under conditions in which the metallic ion of the metal salt is reduced to the metallic state and deposited on the catalytic surface. The use of this process with the products of this invention relies on the catalytic metal sites deposited on the plastic surface as a result of the treatment with the solution of metal salt complex of this invention. A suitable chemical treating bath for the deposition of the nickel coating on a catalytic surface produced in accordance with the process of the invention can comprise, e.g., a solution of a nickel salt in an aqueous hypophosphite solution. Suitable hypophosphites include the alkali metal hypophosphites such as sodium and potassium hypophosphite and the alkaline earth metal hypophosphites such as calcium and barium hypophosphite. Other suitable metal salts for use in the chemical treating bath include the metal salts described hereinbefore with respect to the metal salt complex treatment of the phosphorus treated surface of the invention. Other reducing media include formaldehyde, hydroquinone and hydrazine. Other agents, such as buffering agents, complexing agents, and other additives are included in the chemical plating solutions or baths.

The treated surfaces of the invention can be electroplated by processes known in the art either with or without a prior electroless plating treatment. The articles generally used as the cathode and the metal desired to be plated are generally dissolved in an aqueous plating bath, although other media can be employed. Generally, a solvent metal anode of the metal to be plated can be em-' ployed. In some instances, however, a carbon anode or other inert anode is used. Suitable metals, solutions and conditions for electroplating are described in Metal Finishing Guide Book Directory for 1967, published by Metals and Plastics Publications Inc., Westwood, NJ.

The following examples serve to illustrate the invention but are not intended to limit it. Unless specified otherwise, throughout this specification and claims, all temperatures are in degrees centigrade and parts are understood to be expressed in parts by weight. Adhesion is stated in terms of the force required to pull an inch wide strip of metal away from the substrate surface and is expressed in units of pounds per inch.

EXAMPLES 1-6 Polypropylene samples were immersed in a trichloroethylene rinse bath for 2 minutes at 70 C. and then into a 1.8% phosphorus-trichloroethylene solution for varying amounts of time at 50 C. The samples were then washed with water for one minute at 30 C. and immersed for 15 minutes in a 75 C. metal salt bath. The metal salt bath contained 0.055 M nickel sulfate, 0.22 M triethylene tetraamine and 0.196 M sodium hydroxide. Thereafter the samples were washed with water for 10 minutes at 75 C. and air dried for 30 minutes at 85 C. The transfer times of the samples between the successive baths were one minute each. Each specimen was electroplated with semi-bright nickel, followed by bright nickel and chromium. The phosphorus immersion time, average adhesion and appearance of the final chromium electroplate upon standing are given in Table I.

TABLE I Phos- Appearance at phorus elapsed time immersion (hours) of tim Adheminutes sion 50 3 4.3 C B 3 3.6 C B 6 5.8 C B 6 6.0 C B 6.0 C B 10 6.7 C B NOTE.C Clear (no blistering); B Blistered.

EXAMPLES 7-13 EXAMPLES 14-17 Polypropylene samples were immersed for two minutes in 60 C. trichloroethylene solution and then in a 55 C., 2% phosphorus in trichloroethylene solution for 8 minutes. The samples were then immersed for 6 minutes in a 30 dimethyl formamide solution and then immersed for varying times in a metal salt solution. The metal salt solution contains 0.05 M nickel sulfate, 0.73 M ethylene diamine and 0.457 M sodium hydroxide. The samples were then immersed for 5 minutes in a 70 water bath and air dried for 30 minutes at C. The transfer times between successive solutions were 1 minute each. The resulting polypropylene samples were electroplated with semibright nickel, bright nickel, and chromium. Table III reports the nickel bath solution immersion time, average adhesion and appearance of the final chromium electroplate upon standing.

TABLE III Nickel solution Appearance at elapsed time immer- (hours) sion, Adheminutes sion 16 36 75 156 228 324 15 8.0 C SB SB SB SB B 15 8.6 C VSB SB SB SB B 10 6.3 C C 0 SB SB SB 10 7.8 C C 0 SB SB SB N0'rE.C=Clear (no blistering); VSB =Very slightly blistered; SB= Slightly bllstered: B=B1istered.

EXAMPLES 18-25 The procedure of Examples 14-17 was repeated except that the dimethyl formamide solution was maintained at about 25, the immersion in the nickel solution was for 15 minutes, the temperature of the nickel solution in Examples 18-21 was 65 C. and the nickel solution additiorially contained 3.0 M ammonium hydroxide. The transfer time between successive baths, average adhesion and appearance of the final chromium electroplate is given in Table IV.

TABLE IV Appearance at elapsed Transfer time (hours) of 7 seconds Adhesion 0 230 280 30 13.8 C C C C 30 14.1 C C C C 60 9.8 C O C O 60 10.4 C C C C 30 9.6 O C C C 30 11.2 C C C C 60 11.0 C C C C 60 10.3 C O C G N ore-C Clear (no blistering).

EXAMPLE 26 Samples of polyvinyl chloride, a graft copolymer of polybutadiene, acrylonitrile and styrene, and polyethylene were immersed in a 2% solution of yellow phosphorus in trichloroethylene for 10 minutes and then immersed in a metal salt solution containing silver nitrate, ethylene diamine, sodium hydroxide and ammonium hydroxide. The resulting treated articles were washed with water N ora.-C= Clear (no blistering).

and air dried for 30 minutes at 85 C. Thereafter, the samples were electroless nickel plated and electroplated with Watts nickel. The samples did not develop liquid filled blisters on standing.

EXAMPLE 27 Samples of wood, leather, and polypropylene were immersed in a 2% solution of white phosphorus in trichloroethylene at 70 C. for minutes. The samples were thereafter immersed in a metal salt solution containing bis(ethy1ene diamine) complex of copper sulfate, sodium hydroxide and ammonium hydroxide. The resulting treated samples were water washed and air dried and thereafter electroplated with 0.3 mil of semibright nickel and 1.7 mils of bright acid copper. The electroplated samples did not exhibit a tendency to develop liquid filled blisters upon standing.

Various changes and modifications can be made in the process and products of this invention without departing from the spirit and the scope of the invention. Various embodiments of the invention disclosure herein serve to further illustrate the invention but are not intended to limit it.

I claim:

1. A process comprising subjecting a substrate to elemental white phosphorus to deposit phosphorus at the surface of the substrate and subjecting the resulting treated surface to a solution of a metal salt complex so as to form a metal phosphide wherein said solution of a metal salt complex consists essentially of a metal salt, an amine, an alkali metal hydroxide and ammonium hydroxide and wherein said metal is selected from Groups I-B, II-B, IV-B, V-B, VI-B, VII-B and VIII of the Periodic Table.

2. The process of claim 1 wherein the phosphorus is dissolved in a solvent and wherein droxide is sodium hydroxide.

3. The process of claim 2 wherein the solvent is selected from the group consisting of halogenated hydrocarbons, halocarbons and aromatic hydrocarbons.

4. The process of claim 3 wherein the solvent is trichloroethylene. t

5. The process of claim 1 wherein the metal of said metal salt complex is selected from the group consisting of nickel, copper, and silver.

6. The process of claim 5 wherein said amine is selected from the group consisting of ethylene diamine and triethylene tetraamine.

7. The process wherein the substrate resulting from the process of claim 1 is subjected to electroless metal plating to deposit an electroless conductive coating on the treated surface.

8. The process wherein the substrate resulting from the process of claim 7 is electroplated to deposit an adherent metal coating on the electroless conductive coating.

9. The process wherein the substrate resulting from the process of claim 1 is electroplated to deposit an ad herent coating on the substrate.

the alkali metal hy- References Cited UNITED STATES PATENTS 3,556,956 1/1971 Miller l1747 3,379,539 4/1968 McGrath et a1. 106-1 3,515,649 6/1970 Hepter 117-160 ALFRED L. LEAvrrr, Primary Examiner I. A. BELL, Assistant Examiner US. Cl. X.R.

11747 A, 47 R, 71, R; 106l 

